This invention relates to a rotary motor provided with a device for braking the motor rotation.
A magnetic brake has usually been used as a braking device for rotary motors.
FIG. 1 is a sectional view of a prior art rotary motor having a magnetic brake wherein a field 12 of an electromagnetic brake 10 is fixed on an end face thereof to an end face of a flange 5 at the stator 2 side of the rotary motor 1. An exciting coil 11 and a compression spring 16 are fixed to the other end face of the field 12 and a disc 15 is also fixed thereto at a distance. Between the field 12 and the disc 15 are mounted a rotary plate 14, which is fixed to a rotary shaft 4, and an armature 13 which can be moved parallel to the rotary shaft 4, and which is either pressed against the rotary plate 14 due to the elasticity of the compression spring 16 or separated from the rotary plate 14 due to the electromagnetic force of the exciting coil 11.
In order to allow rotation of the rotor 3 in the above mentioned structure, electricity is applied to the exciting coil 11 to generate an electromagnetic force which is sufficient to overcome the elasticity of the compression spring 16 so that the armature 13 is attracted toward the field 12 to place the rotary plate 14 in a contact free state. In order to apply a braking force on the rotor 3, the electricity is ceased from being applied to the exciting coil 11 to bring the armature 13 in contact with the rotary plate 14 so as to apply a braking force due to the friction between the armature 13 and the rotary plate 14 and between the disc 15 and the rotary plate 14.
The above mentioned prior art magnetic brake requires a large compression spring since the elasticity of the compression spring is used to obtain the frictional braking force, and, moreover, it requires a large exciting coil since the electromagnetic force for attracting the armature must be large enough to overcome the force of the compression spring. Therefore, the size and cost of the rotor motor become larger.
When a rotational angle of the rotary motor is detected by a device, such as a resolver, it is necessary in the prior art to magnetically shield the magnetic brake from the resolver since magnetic flux leakage of the brake tends to adversely affect the output of the resolver.